Sheet discharging device and sheet discharging method

ABSTRACT

A sheet discharging device includes a guide member including a guide surface on which a conveyed sheet is guided, a plurality of sheet discharging rollers, which have an axis, arranged on a guide surface side of the guide member at intervals in a direction crossing a direction in which the sheet is conveyed, the sheet discharging rollers discharging the sheet guided on the guide surface, a sheet discharging tray on which sheets discharged by the sheet discharging rollers are stacked, and a plurality of projecting portions provided on the guide member and projecting from a plane on which the sheet discharging rollers contact the sheet, toward the axis of the sheet discharging rollers, to partly raise the sheet toward the axis of the sheet discharging rollers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-193028, filed Jun. 30, 2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet discharging device mounted in, for example, an auto document feeder in an image forming apparatus to discharge each loaded sheet to a sheet discharging tray or the like, and to a sheet discharging method.

2. Description of the Related Art

Some image forming apparatuses such as copiers are provided with an auto document feeder (ADF). The auto document feeder takes out each of the documents (sheets) stacked in a sheet feeding tray and feeds it to a read position in the image forming apparatus. Then, after an image is read, the auto document feeder discharges the sheet to a sheet discharging tray. The auto document feeder is thus provided with a sheet feeding device that discharges the document from which the image has been read, to the sheet discharging tray. The sheet discharging device comprises a guide member that guides the conveyed document and a sheet discharging roller that discharges the document guided by the guide member, to the sheet discharging tray.

A problem with the conventional sheet discharging device is that a variation in document discharging speed, document size, or the like suppresses the alignment of documents on the sheet discharging tray, that is, the alignment of discharged sheets. The main cause of the suppressed alignment of discharged sheets is that the leading end of a discharged document hangs down owing to gravity and comes into contact with the surface of the documents already discharged onto the sheet discharging tray, thus moving the documents on the sheet discharging tray.

To solve this problem, a technique has been developed which provides a flange portion at one or both of the ends of the sheet discharging roller to corrugate documents. This enables corrugated documents to advance straight more properly when discharged. A discharged document thus first comes into contact with the surface of the documents on the sheet discharging tray at a position farther than the one achieved using a sheet discharging roller without any flange portion. This reduces the time for which and the area over which the discharged document contacts the surface of the documents on the sheet discharging tray. The alignment of discharged documents is thus improved.

A disclosed technique for corrugating documents is adapted for sheet discharging in a fixer in an image forming apparatus (for example, Jpn. Pat. Appln. Publication Nos. 9-240900 and 2002-12355). This technique also uses a flange portion provided on a roller corresponding to a sheet discharging roller to corrugate documents.

However, the manufacture costs of the sheet discharging roller increase when the sheet discharging roller is provided with the flange portion as in the prior art.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a sheet discharging device and a sheet discharging method that can corrugate discharged sheets without increasing manufacture costs.

An aspect of the present invention configures a sheet discharging device as described below.

A sheet discharging device comprises a guide member comprising a guide surface on which a conveyed sheet is guided; a plurality of sheet discharging rollers, which have an axis, arranged on a guide surface side of the guide member at intervals in a direction crossing a direction in which the sheet is conveyed, the sheet discharging rollers discharging the sheet guided on the guide surface; a sheet discharging tray on which sheets discharged by the sheet discharging rollers are stacked; and a plurality of projecting portions provided on the guide member and projecting from a plane on which the sheet discharging rollers contact the sheet, toward the axis of the sheet discharging rollers, to partly raise the sheet toward the axis of the sheet discharging rollers.

Another aspect of the present invention configures a method for discharging a sheet as described below.

A method for discharging a sheet comprises guiding a conveyed sheet along a guide surface to a sheet discharging tray; and allowing projecting portions provided on the guide surface to raise at least a part of the guided sheet in a direction in which the sheet is separated from the guide surface.

The present invention enables discharged sheets to be corrugated without increasing the manufacture costs.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.

FIG. 1 is a front view showing a digital copier according to an embodiment of the present invention;

FIG. 2 is a sectional view showing the internal structure of an auto document feeder according to the embodiment of the present invention;

FIG. 3 is a schematic diagram showing a sheet discharging portion according to the embodiment as viewed from a downstream side in a direction in which the documents are conveyed; and

FIG. 4 is a schematic diagram showing the sheet discharging portion according to the embodiment as viewed from the front of the auto document feeder.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described below in detail with reference to the drawings.

(Configuration of a Digital Copier)

FIG. 1 is a front view showing a digital copier in accordance with an embodiment of the present invention. As shown in FIG. 1, the digital copier comprises an auto document feeder (ADF) 10, a scanner unit 20, and a printer engine section 30.

The auto document feeder 10 loads and supplies each document D to a read position R (described later).

The scanner unit 20 optically reads an image from the document D supplied by the auto document feeder 10 or manually to convert the image into image data.

The printer engine section 30 comprises a charger, a laser unit, a photosensitive drum, a developing device, a transfer roller, and a fixing device (none of them are shown). The charger charges a surface of the photosensitive drum to a predetermined potential. The laser unit forms an electrostatic latent image on the surface of the photosensitive drum on the basis of image data from the scanner unit 20. The developing device develops the electrostatic latent image on the photosensitive drum using toner. The transfer roller transfers the toner image formed on the photosensitive drum to a sheet. The fixing device fixes the toner image transferred to the sheet. In this configuration, the printer engine section 30 copies the document image read by the scanner unit 20 to the sheet.

(Configuration of the Auto Document Feeder 10)

FIG. 2 is a sectional view showing the internal structure of the auto document feeder 10 in accordance with the embodiment of the present invention. As shown in FIG. 2, the auto document feeder 10 is composed of a sheet feeding tray 11 on which a plurality of documents D are placed, a conveying device 12 that takes each of the documents D out of the sheet feeding tray 11 to convey the document D along a conveying path C (described later), and a sheet discharging tray 13 that accommodates a plurality of documents D discharged by the conveying device 12.

The conveying device 12 comprises a first and second guide members 121 and 122. The first and second guide members 121 and 122 comprise smooth guide surfaces 121 a and 122 a, respectively, inside. The U-shaped conveying path C is provided in the gap between the guide surfaces 121 a and 122 a so that the document D can be conveyed along the conveying path C.

The conveying path C connects the sheet feeding tray 11 and the sheet discharging tray 13 together. A read position R is provided in a portion of the conveying path C which is closest to the scanner unit 20; a document image is read at the read position R.

The first guide member 121 is placed outside the second guide member 122. The first guide member 121 has a rectangular opening 121 b formed in its area corresponding to the read position R. This allows the document D conveyed along the conveying path C to be located opposite the scanner unit 20 on passing through the read position R.

The conveying path C has a pickup roller 123, a separate roller 124, a registration roller 125, a first conveying roller 126 a, a second conveying roller 126 b, a stabilizing roller 127, a third conveying roller 126 c, and a sheet discharging roller 128 which are arranged in this order from an upstream side in a direction in which the document D is conveyed.

The pickup roller 123 picks up each of the documents D in the sheet feeding tray 11 and loads it into the conveying path C of the conveying device 12. When a plurality of documents D are loaded by the pickup roller 123, the separate roller 124 passes only the uppermost document D through, while blocking the passage of the remaining documents D. The registration roller 125 registers the document D the passage of which is not blocked by the separate roller 124. The first to third conveying rollers 126 a to 126 c convey the document D registered by the registration roller 125, along the conveying path C. The stabilizing roller 127 stabilizes the behavior of the document D conveyed by the first to third conveying rollers 126 a to 126 c. The sheet discharging roller 128 discharges the document D conveyed by the first to third conveying rollers 126 a to 126 c, from the conveying path C.

Each of the rollers 123 to 128 has a plurality of (in the present embodiment, four) roller pieces around a horizontally supported drive shaft at predetermined intervals. When each of the drive shafts is rotated, all roller pieces provided around the drive shaft rotate concurrently.

Pinch rollers 129 are arranged immediately below the respective sheet discharging roller pieces 128. Each of the pinch rollers 129 is rotatably disposed in a groove portion 121 b of the first guide member 121 (lower guide member 121 c described later). Each of the pinch rollers 129 is contacted with an outer peripheral surface of the sheet discharging roller 128 under pressure by elastic means such as a leaf spring.

The separate roller 124, registration roller 125, first to third conveying roller 126 a to 126 c, and sheet discharging roller 128 constitute respectively roller pairs together with driven rollers arranged opposite them across the conveying path C. For example, the separate roller 124 constitutes a separate roller pair together with a corresponding driven roller.

That portion of the first guide member 121 which lies downstream of the read position R is located below that portion of the second guide member 122 which lies downstream of the read position R. Thus, in the description below, the portion of the first guide member 121 located downstream of the read position R is called a lower guide portion 121 c. The portion of the second guide member 122 located downstream of the read position R is called an upper guide portion 122 c.

FIG. 3 is a schematic diagram showing the sheet discharging portion 120 according to the embodiment as viewed from a downstream side in the direction in which the document D is conveyed. FIG. 4 is a schematic diagram showing the sheet discharging section 120 in accordance with the embodiment as viewed from the front of the auto document feeder.

As shown in FIGS. 3 and 4, the lower guide portion (guide member) 121 c has a guide surface 121 d located below the lowermost portion of the sheet discharging roller 128. It is noted that the guide surface 121 d is a part of the guide surface 121 a. The lower guide portion 121 c comprises a plurality of (in the present embodiment, four) projecting portions 130 located substantially immediately below its drive shaft of the sheet discharging roller 128. The number of projecting portions 130 is not particularly limited.

The projecting portions 130 are disposed so that two of the four sheet discharging roller pieces 128 arranged at the opposite ends of the sheet discharging roller are each sandwiched between the projecting portions 130. The upper end of the each projecting portion 130 projects upward from the lowermost portion of the sheet discharging roller 128.

Each projecting portion 130 comprises a first inclined surface 130 a on its side surface located upstream in the conveying direction of the document D; the first inclined surface 130 a becomes higher as it approaches its downstream end in the conveying direction. Each projecting portion 130 also comprises a second inclined surface 130 b on its top surface which becomes higher as it approaches its downstream end in the conveying direction and which is gentler than the first inclined surface 130 a.

Thus, when the document D reaches the projecting portions 130, parts of the document D which correspond to the projecting portions 130 are scooped up by the first inclined surface 130 a and run onto the second inclined surfaces 130 b. On the other hand, parts of the document D which are corresponding to the roller pieces of the sheet discharging roller 128 are guided by the upper and lower guide portions 121 c and 122 c as they are and then advance between the sheet discharging roller 128 and the pinch roller 129.

As described above, the document D from which a document image has been read is guided by the lower guide portion 121 c. The document D is then discharged onto the sheet discharge tray 13 by the sheet discharging roller 128. The lower guide portion 121 c (including the projecting portions 130), sheet discharging roller 128, and sheet discharging tray 13 thus constitute a sheet discharging portion (sheet discharging device) 120 that discharges the document D from the conveying path C of the conveying device 12. In the present embodiment, a common contact plane P for the sheet discharging roller 128 and pinch roller 129 corresponds to the contact plane between the sheet discharging roller and the sheet in accordance with the present invention.

(Configuration of the Scanner Unit 20)

As shown in FIG. 2, the scanner unit 20 comprises a glass plate (not shown) at a position corresponding to the read position R. The glass plate 21 is colorless and transparent and has a reader (not shown) provided on its scanner unit 20 side. The reader comprises a first carriage, a second carriage, an image forming lens, and a CCD sensor (none of them are shown).

The first carriage is provided with an exposure lamp (not shown) that irradiates the document D passing on a surface of the glass plate, and a first mirror that reflects reflected light from the document surface in a predetermined direction. A second and third mirrors (not shown) are attached to the second carriage to reflect the reflected light from the first mirror in a predetermined direction.

The light emitted from the exposure lamp passes through the glass plate to the surface of the document D passing through the read position R. Then, the light reflected off the document surface passes through the glass plate back to the scanner unit 20. The light is reflected by the first to third mirrors and then guided to the image forming lens. The light converged by the image forming lens is detected by the CCD sensor. The detection signal is used to create image data.

A document glass board (not shown) is provided on the top surface of the scanner unit 20 so that the document D is manually placed on the document glass board. The document glass board is used to read a document image without the use of the auto document feeder 10.

(Operation of Discharging the Document D)

The document D from which the document image has been read is conveyed to the sheet discharging roller 128 while being guided by the upper and lower guides 121 c and 122 c. Once the conveyed document D reaches the projecting portions 130 of the lower guide portion 121 c, parts of the document D which correspond to the projecting portions 130 are scooped up by the first inclined surface 130 a and run onto the second inclined surfaces 130 b. However, parts of the document D which are corresponding to the roller pieces of the sheet discharging roller 128 are guided by guide surfaces 121 d and 122 d of the upper and lower guide portions 121 c and 122 c as they are and then advance between the sheet discharging roller 128 and the pinch roller 129.

This causes the parts of the document D discharged onto the sheet discharging tray 130 to advance in different directions. The document D discharged to the sheet discharging tray 13 has a locally substantially S-shaped cross section, that is, the document is corrugated. Corrugated documents D are sequentially stacked on the sheet discharging tray 13.

An alternate long and short dash line (A) in FIG. 3 shows the advancing direction of the parts of the document D which are corresponding to the projecting portions 130. An alternate long and two short dashes line (B) in FIG. 3 shows the advancing direction of the parts of the document D which are corresponding to the roller pieces of the sheet discharging roller 128.

The document D having run onto the projecting portions 130 is in contact only with the second inclined surface 130 b until it is discharged to the sheet discharging tray 13. Thus, the first inclined surface 130 a is used to scoop up the leading end of the document D when it reaches the projecting portions 130.

(Comparison of Alignment of Discharged Documents)

[Table 1] indicates the misalignment of documents D discharged onto the sheet discharging tray 13 with respect to the conveying direction. [Table 2] indicates the misalignment of the documents D discharged onto the sheet discharging tray 13 with respect to a lateral direction of the documents D, that is, a direction orthogonal to the conveying direction.

In [Table 1] and [Table 2], LT, LT-R, LG, LD, and ST-R denote the sizes of the documents D. The numerical values in [Table 1] and [Table 1] represent the levels of misalignment of the documents D. A larger numerical value indicates a higher level of misalignment. A smaller numerical value indicates a lower level of misalignment. In the present comparison, the speed at which the document D is conveyed is about 210 mm/sec. TABLE 1 Size Present embodiment Prior art LT 30 68 LT-R 5 22 LG 6 18 LD 23 34 ST-R 25 58

TABLE 2 Size Present embodiment Prior art LT 18 45 LT-R 20 5 LG 8 5 LD 18 18 ST-R 5 23

As shown in [Table 1], the auto document feeder 10 according to the present embodiment is far more excellent in the alignment of the discharged documents D than a conventional auto document feeder that uses a flange portion provided on the sheet discharging roller to corrugate the documents.

As shown in [Table 2], the auto document feeder 10 according to the present embodiment is far more excellent, for most document types, in the alignment of the discharged documents D than the conventional auto document feeder that uses the flange portion provided on the sheet discharging roller to corrugate the documents.

[Table 3] indicates the misalignment of the documents D discharged onto the sheet discharging tray 13 with respect to the conveying direction. [Table 4] indicates the misalignment of the documents D discharged onto the sheet discharging tray 13 with respect to the lateral direction of the documents D, that is, the direction orthogonal to the conveying direction.

In [Table 3] and [Table 4], A3, A4, and A4-R denote the sizes of the documents D. The numerical values in [Table 3] and [Table 4] represent the levels of misalignment of the documents D. A larger numerical value indicates a higher level of misalignment. A smaller numerical value indicates a lower level of misalignment. TABLE 3 Basis weight Size 60 g/m² 64 g/m² 80 g/m² A3 23 8 3 A4 30 15 10 A4-R 5 5 15

TABLE 4 Basis weight Size 60 g/m² 64 g/m² 80 g/m² A3 18 13 18 A4 18 18 16 A4-R 20 15 13

As shown in [Table 3] and [Table 4], the misalignment generally falls within a narrow range even with a small variation in misalignment depending on the weight of the document D.

The above results indicate that the auto document feeder 10 according to the present embodiment significantly improves the alignment of the discharged documents D than the conventional auto document feeder that uses the flange portion provided on the sheet discharging roller to corrugate the documents.

(Effects of the Present Embodiment)

The lower guide portion 121 c according to the present embodiment comprises the plurality of projecting portions 130, which project upward from the lowermost portion of the sheet discharging roller 128. The document discharged to the sheet discharging tray 13 thus has an S-shaped cross section, that is, the document is corrugated. This allows the discharged documents D to advance straight more properly.

The present embodiment thus reduces the time for which a document D discharged later rubs against documents D already stacked on the sheet discharging tray 13. The present embodiment also reduces the area over which the document D discharged later comes into frictional contact with the documents D already stacked on the sheet discharging tray 13. This makes the documents D on the sheet discharging tray 13 difficult to move, thus improving the alignment of the documents D on the sheet discharging tray 13.

Furthermore, the projecting portions 130 according to the present embodiment are provided on the lower guide portion 121 c. This drastically reduces the manufacture costs compared to the conventional technique of providing a flange portion at one or both ends of the sheet discharging roller 128.

Moreover, each projecting portion 130 comprises the first inclined surface 130 a on its side surface located upstream in the conveying direction of the document D; the first inclined surface 130 a becomes higher as it approaches its downstream end in the conveying direction. This reduces a possible load on the document D running onto the projecting portions 130. The document D is thus prevented from being damaged.

The lower guide portion 121 c has the guide surface 121 d disposed below the lowermost portion of the sheet discharging roller 128. This allows the parts of the document D corresponding to the projecting portions 130 to rise high on running onto the projecting portions 130. The document D is thus significantly corrugated.

Moreover, the auto document feeder 10 according to the present embodiment significantly improves the alignment of the discharged documents D than the conventional auto document feeder that uses the flange portion provided on the sheet discharging roller to corrugate the documents.

The sheet discharging portion 120 is applicable not only to the auto document feeder but also to, for example, a fixer.

The present invention is not limited to the above embodiments proper. In implementation, the components of the embodiments can be varied without departing from the spirit of the present invention. Further, various inventions can be formed by properly combining a plurality of components disclosed in the above embodiments. For example, some of the components shown in the embodiments can be deleted. Moreover, components of the different embodiments may be properly combined.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. 

1. A sheet discharging device comprising: a guide member comprising a guide surface on which a conveyed sheet is guided; a plurality of sheet discharging rollers, which have an axis, arranged on a guide surface side of the guide member at intervals in a direction crossing a direction in which the sheet is conveyed, the sheet discharging rollers discharging the sheet guided on the guide surface; a sheet discharging tray on which sheets discharged by the sheet discharging rollers are stacked; and a plurality of projecting portions provided on the guide member and projecting from a plane on which the sheet discharging rollers contact the sheet, toward the axis of the sheet discharging rollers, to partly raise the sheet toward the axis of the sheet discharging rollers.
 2. The sheet discharging device according to claim 1, wherein each of the projecting portions is placed near a corresponding one of the sheet discharging rollers.
 3. The sheet discharging device according to claim 1, wherein each of the projecting portions has a first inclined surface formed in an area of the projecting portion which is located upstream of the sheet discharging roller in the conveying direction of the sheet, the first inclined surface being more separate from a plane defined by the guide surface as the first inclined surface approaches its end in the conveying direction of the sheet.
 4. The sheet discharging device according to claim 3, wherein each of the projecting portions has a second inclined surface formed in an area of the projecting portion which corresponds to the sheet discharging roller in the conveying direction of the sheet, the second inclined surface being more separate from the plane defined by the guide surface as the second inclined surface approaches its end in the conveying direction of the sheet, the second inclined surface being gentler than the first inclined surface.
 5. The sheet discharging device according to claim 1, wherein a distance between the plane defined by the guide surface and the axis of sheet discharging rollers is larger than a radius of the sheet discharging roller.
 6. The sheet discharging device according to claim 1, further comprising: a pinch roller which is brought into pressure contact with at least one of the sheet discharging rollers.
 7. The sheet discharging device according to claim 1, wherein the sheet discharging device is applied to an auto document feeder.
 8. A method for discharging a sheet, the method comprising: guiding a conveyed sheet along a guide surface to a sheet discharging tray; and allowing projecting portions provided on the guide surface to raise at least a part of the guided sheet in a direction in which the sheet is separated from the guide surface. 